Two of the youths were in serious condition.
"According to initial information, four teenagers were hurt when the wartime mine blew up near the village of Sirotinskaya in the Ilovlinsky District," police spokeswoman Svetlana Smolyaninova said.
The teens found the land mine Sunday "and started to play with it or take it apart," she said.
The incident occurred in the Volgograd region, formerly Stalingrad, the scene of one of the largest battles of World War II, RIA Novosti reported. The area was heavily mined.